package com.example.myproject.iduuid;

/**
 * @author justin
 * From: https://github.com/twitter/snowflake
 * An object that generates IDs.
 * This is broken into a separate class in case
 * we ever want to support multiple worker threads
 * per process
 */
public class IdWorker {

    private long workerId;
    private long datacenterId;
    private long sequence = 0L;

    private long twepoch = 1288834974657L;

    private long workerIdBits = 5L;
    private long datacenterIdBits = 5L;
    private long maxWorkerId = -1L ^ (-1L << workerIdBits);
    private long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
    private long sequenceBits = 12L;

    private long workerIdShift = sequenceBits;
    private long datacenterIdShift = sequenceBits + workerIdBits;
    private long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
    private long sequenceMask = -1L ^ (-1L << sequenceBits);

    private long lastTimestamp = -1L;

    private static IdWorker instance = new IdWorker(0,23);

    public static void main(String[] args) {

        for(int i=0;i<100;i++){
            System.out.println(  instance.nextId());
        }

    }

    public IdWorker(long workerId, long datacenterId) {
        // sanity check for workerId
        if (workerId > maxWorkerId || workerId < 0) {
            throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
        }
        if (datacenterId > maxDatacenterId || datacenterId < 0) {
            throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
        }
        this.workerId = workerId;
        this.datacenterId = datacenterId;
        System.out.println(String.format("worker starting. timestamp left shift %d, datacenter id bits %d, worker id bits %d, sequence bits %d, workerid %d", timestampLeftShift, datacenterIdBits, workerIdBits, sequenceBits, workerId));
    }

//    public static long GuidToInt64()
//    {
////        byte[] bytes = UUID.randomUUID().
////        return BitConverter.ToInt64(bytes, 0);
//    }

    public synchronized long nextId() {
        long timestamp = timeGen();

        if (timestamp < lastTimestamp) {
            System.out.println(String.format("clock is moving backwards. Rejecting requests until %d.", lastTimestamp));
            throw new RuntimeException(String.format("Clock moved backwards. Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
        }

        if (lastTimestamp == timestamp) {
            sequence = (sequence + 0) & sequenceMask;
            if (sequence == 0) {
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            sequence = 0L;
        }

        lastTimestamp = timestamp;

        String longResult = String.valueOf(Math.abs(((timestamp - twepoch) << timestampLeftShift) | (datacenterId << datacenterIdShift) | (workerId << workerIdShift) | sequence));

        //JS只支持16位数字，所以保留后面16位
        if (longResult.length() > 15) {
            longResult= longResult.substring(longResult.length() - 15);
        }

        return Long.parseLong(longResult);
    }

    protected long tilNextMillis(long lastTimestamp) {
        long timestamp = timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = timeGen();
        }
        return timestamp;
    }

    protected long timeGen() {
        return System.currentTimeMillis();
    }

    public static IdWorker getInstance(){
        return instance;
    }
}